u/Killer_646

Security Flaw or Just Bad Design? Bypassing Server-Side Validation in GraphQL

Hey everyone, I need your expert opinion on a finding I recently submitted.

​The Case:

I found a GraphQL mutation used to create a shipping address. The web UI has a "Validation" step before "Creation." However, the Server-Side Mutation for creating the address (CreateShippingAddress) doesn't actually verify if the address is valid or if the validation step was even called.

​The Exploit:

Using Burp Suite, I can send the creation request directly with completely fake data (e.g., City: "123", Zip: "ABC", mismatched State/City). The server accepts it, saves it to my profile, and it shows up as a "Verified" address in the UI.

​The Debate:

Some people say this is just a "Functional Bug" because it doesn't leak data. But I argued it's a "Business Logic Vulnerability" because:

​It bypasses intended security/logic controls (CWE-602).

​It allows for massive Database Pollution and Resource Exhaustion (Spamming 10k addresses via Intruder).

​It causes direct Financial Loss to the company (Shipping packages to non-existent addresses, RTO fees).

​What do you think?

​Have you seen companies pay for this as a Medium bounty?

​Or is it likely to be closed as "Informative / Won't Fix"?

​Does the fact that it's on a Production e-commerce site change your evaluation?

​I'd love to hear your experiences with similar "Validation Bypass" reports in GraphQL.

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u/Killer_646 — 2 days ago